v4.19.13 snapshot.
diff --git a/include/net/netns/hash.h b/include/net/netns/hash.h
new file mode 100644
index 0000000..16a8424
--- /dev/null
+++ b/include/net/netns/hash.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_NS_HASH_H__
+#define __NET_NS_HASH_H__
+
+#include <asm/cache.h>
+
+struct net;
+
+static inline u32 net_hash_mix(const struct net *net)
+{
+#ifdef CONFIG_NET_NS
+ return (u32)(((unsigned long)net) >> ilog2(sizeof(*net)));
+#else
+ return 0;
+#endif
+}
+#endif